TRADEOFF

FPGA designs can be classified by the type of CLB it uses, there are three different types of basic logic cells: coarse grain, medium grain, and fine grain. (Plus a new type being researched and developed, multigrain?).

Instead of discussing the tradeoff of each individual different FPGA design from all the different companies, I will discuss the tradeoff by the different types of CLB grains.

Design	CLB	Routing	Cost	Switch Matrix	I/O	Efficiency	Performance	Time to Market
Coarse grain	Each CLB is harder to implement since coarse grain CLB architecture is more complex.	Since each CLB in coarse grain is more complex the routing between each cells is also more complex	Since we are simulating  FPGA via VHDL cost of coarse grain is same as fine grain	Since the CLB on coarse grain has higher input and output pins the switch matrices that connects the CLBs are harder to implement switch matrix	The I/O is as complex as fine grain but some coarse grain I/O can be more complex	Less robust place-and-route	Performance of coarse grain is higher than that of fine grain in most cases	Time to market should be longer than fine grain since CLB, and routing is more complex
Medium grain	Between coarse and fine	Between coarse and fine	Same cost	Between coarse and fine	Same as coarse and fine but can be more complex than fine grain	Between coarse and fine	Performance is between those of coarse and fine grain	Between coarse and fine
Fine grain	Simpler CLB architecture, easier to implement	Simpler CLB means simpler routing between each cells	Cost same as coarse grain	CLB has fewer input and output pin so its easier to implement switch matrix	Same as coarse but can be simpler	Fast and robust place-and-route software	Less performance	Shortest time to market
Multigrain	Have both simple CLB and complex CLB, hardest to implement	Routing should be the same as coarse  grain if not a little more harder	Same cost	Should be no harder than a coarse grain but definitely easier than a fine grain		Should be the most efficient design. Most robust.	Performance should be best because it has best of both worlds in technology?	Longest of time to market

Example of coarse grain include xilinx XS40, (for the most part Xilinx uses coarse grain).

Example of fine grain include the Actel Act2 and Act3 CLB.

Multigrain technology is still being researched.